Epicyclic gear system

ABSTRACT

An epicyclic gear system has a sun gear, a ring gear located around the sun gear, and planet gears located between and engaged with sun and ring gears. In addition, it has a carrier including a carrier flange offset axially from the planet gears, carrier pins projecting from the carrier flange into the planet gears, and bearings between the planet gears and the carrier pins so that the planet gears rotate on the pins. Each bearing includes an inner race having tapered raceways presented away from the carrier pin, opposing tapered raceways on the ring gear, and tapered rollers organized in two rows between the raceways. Whereas the carrier pin is cantilevered from the carrier flange, the inner race is cantilevered from the carrier pin remote from the carrier flange, and this insures that the axes about which the planet gears rotate remain parallel to the central axis of the system.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] None

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] None

BACKGROUND OF THE INVENTION

[0003] This invention relates in general to gear systems and, moreparticularly, to an epicyclic gear system.

[0004] The typical epicyclic or planetary gear system basically has asun gear provided with external teeth, a ring gear provided withinternal teeth, and several planet gears located between the sun andring gears and having external teeth which mesh with the teeth on thesun and ring gears. In addition to its gears, the typical system has acarrier to which the planet gears are coupled. Either the sun gear, thering gear, or the carrier is held fast, while power is delivered to andtaken from the remaining two components, and thus power is transferredthrough the planetary system with a change in angular velocity and aninverse change torque.

[0005] The sun and ring gears for all intents and purposes share thesame axis, a central axis, while the planet gears revolve about radiallyoffset axes that are parallel to the central axis—or at least theyshould. Often the offset axes and the central axis are not parallel, andas a consequence the planet gears skew slightly between sun and ringgears. This causes excessive wear along the teeth of the planet, sun andring gears, generates friction and heat, and renders the entire systemoverly noisy.

[0006] The problem certainly exists in straddle carriers. With this typeof carrier the pins on which the planet gears rotate extend between twocarrier flanges in which the pins are anchored at their ends. Thecarrier experiences torsional wind up which causes one carrier flange torotate slightly ahead of the other flange. Not only does this skew thepin for each of the planet gears such that one end liescircumferentially ahead of the other, but it also causes the leading endof the pin to dip toward the central axis and the other end to draw awayfrom the central axis. The end result is a poor mesh between the planetgears and the sun and ring gears, and of course the friction, wear andnoise associated with poorly meshed gears. To counteract this tendency,some planetary systems rely on gears that are wider than necessary andthus offer greater tolerance to skewing along the gear contact. Butthese systems can occupy excessive space and can be quite heavy.

[0007] Other transmissions rely on a double cantilever arrangement atthe pins for their planetary gears to maintain the planet gears and thesun and ring gears properly meshed. In this arrangement the carrier hasa single carrier flange located beyond the ends of the planet gears, andthe carrier pins project from that flange into, and indeed through, thegears. Each carrier pin has one end anchored in the carrier flange andits other end anchored in a sleeve which turns back over the pin tosupport the planet gear. U.S. Pat. No. 3,303,713 to R. J. Hicks shows adouble cantilevered arrangement. Often an antifriction bearing is fittedbetween the sleeve and the planet gear. But antifriction bearingsconsume space, making the planet gears excessively large in diameter,which in turn makes the entire gear system too large and heavy.

SUMMARY OF THE INVENTION

[0008] The present invention resides in an epicyclic gear system thathas a sun gear, a ring gear around the sun gear and at least one planetgear located between and engaged with the sun and ring gears. A carrierflange is offset axially from the planet gear and a carrier pin projectsfrom it into the planet gear. An inner race is attached to the carrierpin remote from the carrier flange, and it has a raceway which ispresented toward a raceway carried by the planet gear. Rolling elementsare organized in a row between the opposed raceways to enable the planetgear to revolve about the carrier pin. The invention also resides in acarrier and bearing for such a gear system.

DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is an exploded perspective view of an epicyclic gear systemconstructed in accordance with and embodying the present invention;

[0010]FIG. 2 is a sectional view of the gear system at one of its planetgears and showing the coupling between the planet gear and the carrier;and

[0011]FIG. 3 is a sectional view of the gear system similar to thesystem of FIG. 2, but showing a modified coupling.

DETAILED DESCRIPTION OF INVENTION

[0012] Referring now to the drawings, a planetary transmission A (FIG.1), which is actually an epicyclic gear system, has the capacity totransmit power of considerable magnitude, given its size and weight. Inshort, it has a high power density. In contrast to some planetarytransmissions, the transmission A relies on meshing gears that are quitenarrow, yet the teeth of those gears remain properly meshed, even whentransmitting substantial power and torque. The transmission A has acentral axis X of rotation about which torque is transferred to thetransmission A and delivered from it. The transmission A basicallyincludes a sun gear 2 having its axis coincident with the central axisX, a ring gear 4 which surrounds the sun gear 2 and shares the axis Xwith it, and planet gears 6 which mesh with and rotate between the sunand ring gears 2 and 4 about axes Y that are offset radially from, yetparallel to, the central axis X. In addition, the transmission A has acarrier 8 to which the planet gears 6 are coupled, and the carrier 8likewise shares the axis X.

[0013] Referring more specifically to the sun gear 2, it is attached toa shaft 12 or some other supporting structure with which it normallyrotates, but it may be fixed against rotation in some installations. Thesun gear 2 has external teeth 14 which are presented outwardly away fromthe axis X.

[0014] The ring gear 4 is typically fixed, and thus does not rotate,although it may rotate in some installations. In any event, the ringgear 4 has internal teeth 18 which are presented inwardly toward theaxis X and toward the external teeth 14 on the sun gear 2 and lieconcentric with them. The ring gear 4 may be part of or integrated intoa housing for the transmission A.

[0015] An annular space exists between the sun and ring gears 2 and 4,and the planet gears 6 occupy that space. Each has external teeth 22which mesh with the external teeth 14 or the sun gear 2 and the internalteeth 18 on the ring gear 4. Thus, when the sun gear 2 rotates relativeto the ring gear 4 about the axis X or vice versa, the planet gears 6will revolve, each about its offset axis Y that lies parallel to thecentral axis X. The planetary gears 6 are hollow, with each having tworaceways 24 (FIG. 2) which taper downwardly to an intervening surface 26located midway between the ends of the gear 6. The large ends of theraceways 24 for each planet gear 6 open out of the ends of the gear 6.

[0016] The carrier 8 includes (FIG. 1) a carrier flange 30 to which allof the planet gears 6 are coupled, it being offset axially beyondcorresponding ends on each of the gears 6. Normally, the carrier 8rotates about the axis X, although it may remain fixed in someinstallations. When the carrier 6 rotates, it is usually coupled to ashaft 32 that lies along the axis X. In addition to the carrier flange30, the carrier 6 has carrier pins 34 which project from the flange 30into the planet gears 6, their axes generally corresponding to the axesY of rotation for the planet gears 6.

[0017] More specifically, the carrier flange 30 opposite each planetgear 6 has a tapered hole 36 (FIG. 2). The carrier pins 34, on the otherhand, have tapered surfaces 38 which lead out to threaded ends 40. Thetapered surfaces 38 conform in configuration to the tapered holes 36 inthe flange 30 and indeed fit snugly into the tapered holes 36 so thatthe pins 34 project from the face of the carrier flange 30 that ispresented toward the planet gears 6. The threaded ends 40 project beyondthe other face of the carrier flange 30 where they are engaged by nuts42 which are turned down snugly against that face. This lodges thecarrier pins 34 at their tapered surfaces 38 firmly in the carrierflange 30. Thus, each pin 34 is, in effect, cantilevered from thecarrier flange 30.

[0018] Each carrier pin 34 projects through its planet gear 6, and atthe opposite end of the gear 6, that is the end remote from the carrierflange 30, is fitted to an inner race 46 which the planet gear 6 alsoencircles. The inner race 46 has an end wall 48 and a sleeve 50 formedintegral with the end wall 48. Indeed, the sleeve 50 turns backwardlyfrom the end wall 48 into the interior of the gear 6 and thus encirclesthe carrier pin 34. The end wall contains a bore 52 into which the endof the carrier pin 34 fits with an interference fit. At its very end thecarrier pin 34 is joined to the end wall 48 along a weld 54. Thus, theinterference fit together with the weld 54 secure the inner race 46firmly to the carrier pin 34. The interior surface of the sleeve 50 issomewhat larger than the carrier pin 34, and as a consequence the innerrace 46 at its end wall 48 is cantilevered from the remote end of thecarrier pin 34.

[0019] The sleeve 50 of the inner race 46 lies within the interior ofthe planet gear 6 and has two tapered raceways 56 which taper downwardlyto a separating rib 58. The raceways 56, which have their centers alongthe axis Y, are presented outwardly away from the axis Y and toward theraceways 24 on the gear 6, each raceway 56 on the inner race 46 beingopposite one of the raceways 24 on the gear 6. On the other hand, theseparating rib 58 lies opposite the intervening surface 26 of the gear6. Each raceway 56 on the inner race 46 tapers in the same direction asthe raceway 24 toward which it is presented on the planet gear 6. Theraceway 56 closest to the carrier flange 30 leads out to a thrust rib 60that is formed integral with the sleeve 50 of the inner race 26. Theother raceway 56 leads out to a cylindrical mounting surface 62 thatsurrounds the end wall 48. The mounting surface 62 has a rib ring 64fitted to it with an interference fit and further secured with a weld 66at its end. The rib ring 64 extends axially from the weld 66 to thelarge end of the tapered raceway 56, so the rib ring 64 forms anotherthrust rib, similar function to the rib 60 at the end of the inner race46 that is remote from the carrier flange 30.

[0020] The annular region between each planet gear 6 and inner race 46that the gear 6 surrounds is occupied by rolling elements in the form oftapered rollers 70 organized into two rows. One row lies along theintegral thrust rib 60 that is adjacent to the carrier flange 30 andcontacts the opposed raceways 24 and 56 at that end, while the other rowlies along the rib ring 64 that surrounds the end wall 48 of the innerrace 46 and contacts the raceways 24 and 56 at that end. Indeed, thetapered rollers 70 contact the raceways 24 and 56 along their taperedside faces, there being generally line contact here. They also bearagainst the thrust rib 60 and rib ring 64 at their large end faces. Thethrust rib 60 and rib ring 64 prevent the rollers 70 from moving up theraceways 24 and 56 and being expelled from the annular region betweenthe planet gear 6 and the inner race 46. The rollers 70 of each row areon apex, meaning that the conical envelopes in which the side faces ofthe rollers 70 of a row lie will have their apices located at a commonpoint along the axis Y. This produces pure rolling contact between theside faces of the rollers 70 and the raceways 24 and 56. While therollers 70 of each row may be separated with a cage, preferably they arenot so confined. This enables each row to contain the maximum number ofrollers 70.

[0021] The rollers 70 together with the inner race 46 and the raceways24 on the planet gear 6 form a double row tapered roller bearing 72 thatcouples the planet gear 6 to the carrier pin 34 about which the gear 6rotates. Indeed, the bearing 72 has the capacity to facilitate rotationof the planet gear 6 about the axis Y with minimal friction, whileconfining the gear 6 radially and axially on the carrier pin 34. Inother words, the bearing 72 takes thrust loading in both axialdirections. Moreover, the bearing 72 is set to a condition of lightpreload, and as a consequence no axial or radial clearances exist withinit. This enables the gear 6 to rotate on the carrier pin 34 withoutaxial or radial free motion and without wobbling.

[0022] The carrier pins 34 possess a measure of flexibly and indeed willflex well within their elastic limits when torque is transferred throughthe planet gears 6. The double cantilever arrangement enables the axes Yto remain parallel to the axis X, and hence the planet gears 6 remainproperly meshed with the sun and ring gears 2 and 4. Thus, the planetgears 6, and likewise the sun and ring gears 2 and 4, need not beexcessively wide to account for off-center gear contact.

[0023] To assemble the carrier 8, each carrier pin 34 at its cylindricalend is forced into the bore 52 in the carrier flange 48 of the innerrace 46 for that pin 34. Then the carrier pin 34 at its end is welded tothe end wall 48, producing the weld 54. Thereupon, the rollers 70 forthe row remote from the end wall 48 are placed along the raceway 56 thatleads up to the thrust rib 60, with the large end faces of those rollersbeing 70 against the rib 60. Next the planet gear 6 is installed overthe inner race 46 and the row of rollers 70 on that race 46. The leadingraceway 24 in the gear 6 seats against the side faces of those taperedrollers 70. This leaves an annular void between the raceways 24 and 56at the opposite end planet gear 6. More rollers 70 are inserted intothis void with their small ends leading, thus creating a second row ofrollers 70 having their large ends located along the end of the mountingsurface 62 for inner race 46. With the gear 6 and the two rows ofrollers 70 in place around the inner race 46, the rib ring 64 is forcedover the mounting surface 62 on the inner race 46, and advanced towardthe large ends of the rollers 70 that are at the mounting surface 62. Asthe rib ring 64 approaches the large end faces of the rollers 70, thegear 6 is rotated to insure that the rollers 70 of the two rows seatagainst the raceways 24 and 56 and along the thrust rib 60 and rib ring64. After the rib ring 64 comes against the large end faces of therollers 70 in the row that is along it, the bearing 72 will enterpreload. The advance continues a short distance until the bearing 72acquires the proper preload. Then the rib ring 64 is welded to the innerrace 46, producing the weld 66. The gear 6, rollers 70, inner race 46and carrier pin 34 34 constitute a subassembly 76, and enoughsubassemblies 76 are produced in the foregoing manner to complete thecarrier 8.

[0024] Within each subassembly 76 the tapered surface 38 of the carrierpin 34 extends beyond the open end of the sleeve 50 for the inner race46 and beyond the corresponding end of the planet gear 6 as well. Thetapered surface 38 of the carrier pin 34 is inserted into one of thetapered holes 36 of the carrier flange 30, whereupon one of the nuts 42is engaged with the threaded end 40 that projects out of the flange 30.The nut 42 is turned down firmly against the carrier flange 30 to drawthe tapered surface 38 of the carrier pin 34 snugly into the taperedhole 36. This secures the carrier pin 34 and inner race 46 firmly to thecarrier flange 30. The remaining subassemblies 76 are installed on thecarrier flange 30 in a like manner.

[0025] With the carrier 8 so assembled, it is installed over the sungear 2 and into the ring gear 4 such that the external teeth 22 on theplanet gears 6 engage the external teeth 14 in the sun gear 2 and theinternal teeth 18 on the ring gear 4.

[0026] When torque is applied to the shaft 12 to rotate the sun gear 2,the planet gears 6 revolve and move along the ring gear 4, thusimparting rotation to the carrier 8 and the shaft 32 extended from it.The angular velocities of the two shafts 12 and 32 differ and with thatdifference a change in the torque ensues. Of course, the torque may beapplied to the shaft 32 and taken from the shaft 12. Actually, any oneof the sun gear 2, ring gear 4 and carrier 8 may be held fast and torquedelivered to and taken from the remaining two components.

[0027] In a modified subassembly 78 (FIG. 3) the carrier pin 34 isformed integral with the inner race 46.

[0028] The cantilever of the carrier pins 34 from the carrier flange 30and the cantilever of the inner races 46 from the carrier pins 34, thatis the so-called “double cantilever”, insures that the axes Y ofrotation for the ring gears 6 remain parallel to the center axis X. As aconsequence, the ring gears 6 do not require excessive width to resistskewing. The inner races 46, being mounted directly on the carrier pins34, instead of on intervening components, together with the integrationof the outer raceways 24 into the planet gears 6, enables the bearings72 to be of a diameter that is smaller than the diameters of bearings inmore conventional epicyclic gear systems. This, in turn, can permit useof smaller sun and ring gears 2 and 4, and otherwise render the entiretransmission highly compact and light in weight.

[0029] In lieu of a double row tapered roller bearing 70, each planetgear 6 may be coupled to its carrier pin 34 on the carrier 8 with adouble row angular contact ball bearing or even with a cylindrical orspherical roller bearing. Also, more or less than four planet gears 6may be used between the sun gear 2 and ring gear 4. EPICYCLIC GEARSYSTEM A transmission X axis Y axes  2 sun gear  4 ring gear  6 planetgears  8 carrier 12 shaft 14 external teeth 18 internal teeth 22external teeth 24 raceways 26 intervening surface 30 carrier flange 32shaft 34 carrier pins 36 tapered hole 38 tapered surface 40 threadedends 42 nut 46 inner race 48 end wall 50 sleeve 52 bore 54 weld 56tapered raceway 58 separating member 60 thrust rib 62 mounting surface64 rib ring 66 weld 70 tapered rollers 72 bearing 76 subassembly 78subassembly

What is claimed is:
 1. An epicyclic gear system comprising: a sun gearlocated along a central axis; a ring gear located around the sun gearand sharing the central axis with the sun gear; at least one planet gearlocated between and engaged with the sun and ring gears for rotationabout an offset axis, the planet gear having a raceway that is presentedtoward the offset axis; and a carrier coupled to the planet gear andincluding a carrier flange, a carrier pin projecting from the flangeinto the planet gear, an inner race attached to the carrier pin remotefrom the carrier flange and also located within the ring gear where ithas a raceway presented outwardly away from the offset axis and towardthe raceway carried by the ring gear, and rolling elements located in arow between and contacting the raceways on the ring gear and inner race.2. A gear system according to claim 1 wherein the carrier pin iscantilevered from the carrier flange, and the inner race is cantileveredfrom the carrier pin at a location remote from the carrier flange.
 3. Agear system according to claim 2 wherein the inner race includes asleeve which surrounds, but is spaced from the carrier pin, and an endwall connected to the sleeve at one end of the sleeve; wherein theraceway for the inner race is on the sleeve; and wherein the carrier pinis connected to the inner race at the end wall of the inner race.
 4. Agear system according to claim 3 wherein the end wall and the sleeve areformed integral.
 5. A gear system according to claim 4 wherein thecarrier pin and the end wall of the inner race are formed integral.
 6. Agear system according to claim 3 wherein the raceway on the planet gearis one of two outer raceways which are located oblique to the offsetaxis and are inclined in opposite directions; wherein the raceway on theinner race is one of two inner raceways that are oriented oblique to theoffset axis and inclined in opposite directions, one of the innerraceways being located within and inclined in the same direction as oneof the outer raceways and the other inner raceway being located withinand inclined in the same direction as the other outer raceway; andwherein the rolling elements are arranged in two rows between the outerand inner raceways.
 7. A gear system according to claim 6 wherein theraceways are tapered; wherein the rolling elements are tapered rollers;wherein the sleeve of the inner race has thrust ribs at the large endsof the tapered inner raceways; and wherein one of the thrust ribs fitsover the inner race as an initially separate component.
 8. In anepicyclic gear system including a sun gear located along a central axis,a ring gear located around the sun gear and sharing the central axis;planet gears located between and engaged with the sun and ring gears forrotation about offset axes that are located around the central axis; acarrier coupled with the planet gears and including a carrier flangeoffset axially from the planet gears, carrier pins cantilevered from thecarrier flange and projected into the planet gears along the offsetaxes, there being a separate carrier pin for each planet gear, an innerrace cantilevered from each carrier pin remote from the carrier flangeand located within the planet gear into which the pin projects, a firstinner raceway carried by each inner race and presented outwardly awayfrom the offset axes for that inner race, a first outer raceway carriedby the planet gear that is located around the carrier pin and presentedinwardly toward the offset axes and toward the first inner raceway onthe inner race; and rolling elements located between and contacting thefirst raceways.
 9. The combination according to claim 8 and furthercomprising a second inner raceway carried by the inner race around eachcarrier pin and presented outwardly away from the offset axes for thatcarrier pin, a second outer raceway carried by the planet gear that isaround the carrier pin and presented inwardly toward the offset axes andthe second inner raceway; and wherein the rolling elements are arrangedin two rows, with one row being between the first inner and outerraceways and the other row being between the second inner and outerraceways.
 10. The combination according to claim 9 wherein the racewaysare oblique to the offset axes; and wherein the first inner and outerraceways are inclined in the same direction and the second inner andouter raceways are inclined in the same direction, which direction isopposite to the direction of inclination of the first raceways, wherebythe rolling elements in the row between the first raceways will transferthrust loads in one axial direction and the rolling elements in the rowbetween the second raceways will transfer thrust loads in the oppositeaxial direction.
 11. The combination according to claim 10 wherein theraceways are tapered and the rolling elements are tapered rollers. 12.The combination according to claim 11 wherein the first and secondraceways taper inwardly toward each other so that the large ends of therollers in the row between the first raceways are presented away fromthe large ends of the rollers in the row between the second raceways.13. The combination according to claim 12 wherein the inner race hasthrust ribs at the large ends of the inner raceways; and wherein one ofthe thrust ribs is a rib ring formed as a separate component that isinstalled on the inner race after the rollers are placed between theplanet gear and the inner race.
 14. The combination according to claim10 wherein inner race includes a sleeve on which the inner raceways arelocated and an end wall at one end of the sleeve; the end wall beingattached firmly to the carrier pin remote from the carrier flange withthe sleeve surrounding, but being spaced from the carrier pin.
 15. In anepicyclic gear system having a central axis and a planet gear thatrotates about an offset axis that is offset radially from the centralaxis, the improvement comprising: a carrier flange located beyond oneend of the planet gear, a carrier pin projecting from the carrier flangeinto the planet gear such that it is cantilevered from the carrierflange; and a bearing located between the carrier pin and the planetgear for coupling the planet gear to the carrier flange and enabling theplanet gear to rotate about the offset axis, the bearing including aninner race which is attached to the carrier pin remote from the carrierflange and includes a sleeve which surrounds the carrier pin, yet isspaced from the pin, the sleeve having a first raceway that is presentedoutwardly away from the offset axis for the planet gear, the bearingalso including a first outer raceway that is carried by the planet gearand is presented inwardly toward the offset axis and the first innerraceway, the bearing further including rolling elements arranged in arow between the first inner and outer raceways.
 16. The combinationaccording to claim 15 wherein the inner race also includes an end wallextended between the sleeve and the carrier pin and attached firmly tothe pin remote from the carrier, whereby the inner race is cantileveredfrom the carrier pin.
 17. The combination according to claim 15 whereinthe first inner and outer raceways are inclined in the same directionwith respect to the offset axis; wherein the inner race has a secondinner raceway that is presented outwardly away from the offset axis andis inclined with respect to the offset axis in a direction opposite theinclination of the first raceways, and the bearing also includes asecond outer raceway carried by the planet gear and presented inwardlytoward the second inner raceway and inclined with respect to the offsetaxis in the same direction as the second inner raceway; and wherein therolling elements are organized in first and second rows, the rollingelements of the first row being between the first raceways and therolling elements of the second row being between the second raceways.18. The combination according to claim 17 wherein the raceways aretapered and the rolling elements are tapered rollers; wherein the innerrace has a thrust rib at the large end of the first inner raceway withthe rib projecting beyond the first inner raceway, the large ends of therollers in the first row being against the thrust rib, and the innerrace also has a mounting surface at the large end of the second innerraceway with the mounting surface having a diameter no greater than thediameter of the large end of the second inner raceway, and wherein aninitially separate rib ring is located around the mounting surface onthe inner race and projects outwardly beyond the large end of the secondinner raceway, the large ends of the tapered rollers in the second rowbeing against the rib ring.
 19. The combination according to claim 18wherein the inner race also includes an end wall extended between thesleeve and the carrier pin and attached firmly to the carrier pin remotefrom the carrier flange, whereby the inner race is cantilevered from thecarrier pin.
 20. The combination according to claim 19 wherein the endwall and sleeve of the inner race are integral.
 21. In an epicyclic gearsystem having a central axis and a planet gear offset radially from thecentral axis where it is located between and engaged with other gears,the improvement comprising: a carrier flange located beyond one end ofthe planet gear; a carrier pin projecting from the carrier flange intothe planet gear, the carrier pin being offset from the central axis andcantilevered from the carrier flange; an inner race attached to the pinremote from the carrier flange such that the inner race is cantileveredfrom the pin, the inner race having an inner raceway that is presentedoutwardly away from the carrier pin; an outer raceway carried by theplanet gear and presented toward the inner raceway on the inner race;and rolling elements located in a row between and contacting the innerand outer raceways.
 22. The combination according to claim 21 whereinthe inner race includes a sleeve which surrounds the carrier pin andcarries the inner raceway, yet is spaced from the pin, and an end wallat one end of the sleeve, with the inner race being attached to thecarrier pin at the end wall.